Formatting log still takes considerable computing, especially when working on embedded system, where your cpu is only a few hundreds MHz.

You don't need to format the log on-device. You can push a binary representation and format when you need to display it. Look a 'defmt' for an example of this approach. Logging overhead in the path that emits the log messages can be tens of instructions.

Hence the mention of binary stuff.... We use ftrace in linux and we limit ourselves a lot on what we "print".